1. Field of the Invention
The invention is directed to an active rear axle kinematics disclosed by German published application 36 24 457 and in corresponding U.S. Pat. No. 4,785,065 for a motor vehicle also steered at the rear wheels thereof, whereby the rear wheel steering angle or angles are set by an electronically controlled actuator according to rated values for the rear wheel steering angle or angles or, respectively, rated values which can be derived therefrom whereby these rated values, or respectively, the rear wheel steering angles are calculated at least from
sampled values for the respective front axle steering angle and/or values which can be derived therefrom, PA1 a potentially speed-dependent derivative action time constant, PA1 a potentially speed-dependent delay time constant, and PA1 a potentially speed-dependent co-steering factor. PA1 to enable a precise solution despite an extremely short calculating time, as well as PA1 to be able to reduce the computational outlay in the process computer and, as a result hereof, to also be able to reduce the memory requirement of this process computer. This object is achieved by the a digital filter is provided for the purpose of determining the rated values for the rear axle steering angle or angles, the digital filter being dimensioned according to a difference equation, whereby the difference equation, in turn, corresponds to a differential equation for the steering kinematics while satisfying Shannon's sampling theorem.
2. Description of the Related Art
In the known rear axle kinematics, a differential equation is solved with a process computer for calculating the rear axle steering angle. Such digital equations can usually be solved by iterative methods on the basis of digital, i.e., non-analog methods. The problem thereby derives that the solution is solved with adequate precision only after a plurality of iteration steps--this plurality being still unknown at the beginning of the calculation. In situations wherein one must react quickly, this means that the computer no longer finds a result in time or, respectively, that one must count on imprecise solutions dependent on how many iteration steps were capable of being carried out.
In an automobile, this can lead to problems precisely in dangerous situations when abrupt steering is carried out. The iterative solution of a differential equation also requires a relatively high memory requirement for the process computer.